A number of methods of processing oil-shale or tar sands by distillation or carbonisation in order to obtain the organic material therein have been put forward. Generally for example oil-shale is processed after preheating in a distillation or carbonation apparatus or retorting zone (in this specification the terms carbonisation and distillation are used generally interchangeably and such terms are also used interchangeably with the term "retorting"). In this operation, at temperatures of about 250.degree. to 900.degree. C., besides fluid organic compounds and gaseous products, there are also formed carbon-bearing solid compounds (residual coke) which generally remain in the oil-shale after the carbonisation treatment, in amounts of from 5 to 10%. These substances are usually burnt and the waste heat obtained in this way is used in various ways in the process. Thus, all or part of the hot combustion gas may be passed as a heat-carrier agent into the retorting zone for direct heat exchange (as disclosed in U.S. Pat. No. 3,297,562) or for indirect heat exchange (see U.S. Pat. No. 3,384,569), or alternatively used for preheating the oil-shale (see U.S. Pat. No. 3,475,319). The hot shale which has been burnt off and which is therefore substantially free from carbon can be used as a heat-carrier agent in the process (see German laid-open application No. 2,429,767), but this requires correspondingly expensive equipment for separating it off. Therefore, it is frequently subjected to cooling, thereby regaining the heat content therefrom, and then removed from the process.
Methods of producing shale-oil or oils from tar sand have also been disclosed, wherein the retorting operation is performed in the presence of hydrogen. The oils produced in this way are of improved quality as they are more highly saturated and contain smaller amounts of sulphur and nitrogen compounds than oils which are produced without hydrogenation. A particular advantage of such a hydrogenating carbonisation or distillation operation is that it makes it possible to produce a larger amount of the desired liquid products and a smaller amount of residual coke as, by virtue of the presence of hydrogen, the formation of unsaturated hydrocarbon polymers and carbon residues is suppressed or reduced. Various modes of operation have been proposed for carrying out the hydrogenating carbonisation or distillation step. Frequently, the method is performed using suspensions or slurries of the ground oil-shale in heavy oils resulting from the process (U.S. Pat. Nos. 3,565,751) and 3,617,469). Catalytically effective compounds are also used in this operation (U.S. Pat. No. 3,565,751). It has also been suggested that the hydrogenating treatment of oil-shale should be performed with the addition of water (see U.S. Pat. No. 3,617,472). This method provides a comparatively high yield in respect of the products desired and such a low residual carbon content, about 3%, in the processed shale, that it did not seem worthwhile to burn off the residual carbon content. It is therefore removed from the process after cooling.